Lipase is widely used in the esterification reaction between various carboxylic acids such as fatty acids and alcohols such as monoalcohols and polyalcohols; or the transesterification reaction between multiple carboxylic esters. Among them, a transesterification reaction is an important technology to modify animal and vegetable fats and oils, and to produce esters of various fatty acids, sugar esters and steroid. When lipase which is a hydrolase of fats and oils is used as a catalyst of these reactions, the transesterification reaction can be conducted under the mild condition of room temperature to around 70° C. Thus, as compared with conventional chemical reactions, lipase not only inhibits side reactions and decreases energy costs, but also has high safety since lipase as a catalyst is a natural product. Further, objective compounds can be effectively produced because of the substrate specificity and place specificity thereof. However, though lipase powder is directly used in a transesterification reaction, the activity of lipase does not generally sufficiently express. In addition, it is difficult to uniformly disperse lipase which is basically soluble in water to an oil-based raw material, and also difficult to collect it. Accordingly, it is common that lipase is immobilized on a certain carrier such as an anion-exchange resin (Patent Literature 1), a phenol adsorption resin (Patent Literature 2), a hydrophobic carrier (Patent Literature 3), a cation-exchange resin (Patent Literature 4) and a chelate resin (Patent Literature 5), and used in an esterification or transesterification reaction.
However, since the lipase activity decreases when lipase is immobilized on a carrier, various technologies have been developed using lipase powder.
More specifically, the method is proposed which comprises the steps of dispersing lipase powder in a raw material containing an ester(s) in the presence or absence of an inactive organic solvent so that 90% or more of the particle size of the dispersed lipase powder particles is kept within 1 to 100 μm in the transesterification reaction; and then conducting the transesterification reaction (Patent Literature 6). Further, it is also proposed to use enzymatic powder which is obtained by drying an enzymatic solution containing a phospholipid(s) and lipid-soluble vitamin(s) (Patent Literature 7).
Meanwhile, since lipase which is an enzyme is expensive, it is collected after the completion of the reaction and repeatedly used, and it is first discarded when the lipase activity considerably decreases. However, if the decreased lipase activity can be recovered, usability of lipase would dramatically improve. Thus, from the industrial viewpoint, the effective method of recovering lipase activity has been desired to be developed.
Patent Literature 1: JP-A 60-98984
Patent Literature 2: JP-A 61-202688
Patent Literature 3: JP-A 2-138986
Patent Literature 4: JP-A 3-61485
Patent Literature 5: JP-A 1-262795
Patent Literature 6: JP-B 2668187
Patent Literature 7: JP-A 2000-106873